Like many cellular processes,
muscular contraction operates, Allen explains, by means of a calcium-dependent
switch. When a muscle cell receives a neural impulse to contract, calcium
is released in the cell. Key to the contraction process is a three-component
protein complex--troponin C, troponin I, and troponin T.

The three-part protein complex
wraps in a strand around the thin filaments of muscle cells, which are
made of interdigitated thin and thick filaments. (See photo.)

When calcium is released within
the cell, troponin C binds with the calcium, causing the entire troponin
strand to retract, allowing the thick and thin muscle filaments to come
into contact. When this happens, the rowing-like motion of thick-filament
proteins tugs on the thin filaments, contracting the muscle.

Allen and students pursuing
research
projects in his lab will examine the mechanism by which troponin I performs
its functions in the switch.